Add ability to load test remote Yara config

[sgress454]

From the parent ticket:

We need to add support to osquery-perf to simulate osquery requesting YARA rules using the new authenticated endpoint (to load test thousands of agents using this new endpoint).
osquery-perf: https://github.com/fleetdm/fleet/blob/main/cmd/osquery-perf/agent.go

The plan here is to update the runLiveQuery implementation so that it branches based on the contents of the live request. If it's determined to be a request for a Yara scan with a remote rule (i.e. it has "FROM yara" and "sigurl" in it) then we'll do the appropriate request to the Fleet instance to get the rule, and send a mock YARA response. Otherwise we'll send the regular mock response. Updating the runLiveQuery code means we can take advantage of the existing options around simulating failure and empty result sets.